U.S. patent number 10,359,505 [Application Number 15/124,045] was granted by the patent office on 2019-07-23 for optical imaging modules and optical detection modules including a time-of-flight sensor.
This patent grant is currently assigned to ams Sensors Singapore Pte. Ltd.. The grantee listed for this patent is ams Sensors Singapore Pte. Ltd.. Invention is credited to Stephan Beer, Bernhard Buettgen, Sophie Gode, Bassam Hallal, Michael Lehmann, Daniel Perez Calero, Miguel Bruno Vaello Panos.
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United States Patent |
10,359,505 |
Buettgen , et al. |
July 23, 2019 |
Optical imaging modules and optical detection modules including a
time-of-flight sensor
Abstract
The present disclosure describes optical imaging and optical
detection modules that include sensors such as time-of-flight (TOF)
sensors. Various implementations are described that, in some
instances, can help reduce the amount of optical cross-talk between
active detection pixels and reference pixels and/or can facilitate
the ability of the sensor to determine an accurate phase difference
to be used, for example, in distance calculations.
Inventors: |
Buettgen; Bernhard (Adliswil,
CH), Vaello Panos; Miguel Bruno (Zurich,
CH), Beer; Stephan (Schaffhausen, CH),
Lehmann; Michael (Winterthur, CH), Perez Calero;
Daniel (Zurich, CH), Gode; Sophie (Zurich,
CH), Hallal; Bassam (Thalwil, CH) |
Applicant: |
Name |
City |
State |
Country |
Type |
ams Sensors Singapore Pte. Ltd. |
Singapore |
N/A |
SG |
|
|
Assignee: |
ams Sensors Singapore Pte. Ltd.
(Singapore, SG)
|
Family
ID: |
52727098 |
Appl.
No.: |
15/124,045 |
Filed: |
March 13, 2015 |
PCT
Filed: |
March 13, 2015 |
PCT No.: |
PCT/EP2015/055357 |
371(c)(1),(2),(4) Date: |
September 07, 2016 |
PCT
Pub. No.: |
WO2015/136099 |
PCT
Pub. Date: |
September 17, 2015 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20170090018 A1 |
Mar 30, 2017 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61987045 |
May 1, 2014 |
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61981235 |
Apr 18, 2014 |
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61953089 |
Mar 14, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01S
7/4813 (20130101); G01S 7/4915 (20130101); G01S
17/89 (20130101); G01S 7/4918 (20130101); G01S
7/497 (20130101); G01S 17/894 (20200101); G01J
1/0214 (20130101); G01J 1/0422 (20130101); G01J
2001/4247 (20130101) |
Current International
Class: |
G01C
3/08 (20060101); G01S 7/491 (20060101); G01S
7/497 (20060101); G01S 17/89 (20060101); G01S
7/481 (20060101); G01J 1/04 (20060101); G01J
1/42 (20060101); G01J 1/02 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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102652431 |
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Aug 2012 |
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CN |
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102713572 |
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Oct 2012 |
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CN |
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1 195 617 |
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Oct 2002 |
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EP |
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2 017 651 |
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Jan 2009 |
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EP |
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201312144 |
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Mar 2013 |
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TW |
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Other References
Australian Patent Office, International Search Report and Written
Opinion for International Patent Application No. PCT/EP2015/055357,
dated Nov. 23, 2015. cited by applicant .
Intellectual Property Office of Taiwan, Search Report issued in
Taiwan Application No. 104108361, dated Jan. 2, 2019, 1 page. cited
by applicant.
|
Primary Examiner: Abraham; Samantha K
Attorney, Agent or Firm: Fish & Richardson P.C.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION(S)
This application claims the benefit of priority of the following
U.S. Provisional Patent Application Ser. Nos. 61/953,089 filed on
Mar. 14, 2014; Ser. No. 61/981,235 filed on Apr. 18, 2014; and Ser.
No. 61/987,045 filed on May 1, 2014. The contents of the prior
applications are incorporated herein by reference.
Claims
What is claimed is:
1. An optoelectronic module comprising: an illumination source; a
sensor including spatially distributed detection pixels and at
least one reference pixel; an optics member disposed over the
illumination source and the sensor, the optics member having a
first transmissive region over the illumination source and a second
transmissive region over the detection pixels; a light barrier
separating an emission chamber of the module from a detection
chamber of the module, wherein the illumination source and the at
least one reference pixel are in the emission chamber, and wherein
the detection pixels are in the detection chamber; and a partially
reflective coating on a surface of the first transmissive region
over the illumination source wherein the coating is partially
reflective with respect to a wavelength detectable by the reference
pixel and is arranged such that some light from the illumination
source is reflected by the coating toward the at least one
reference pixel.
2. The optoelectronic module of claim 1 including a partially
reflective coating on a surface of the first transmissive region
facing the illumination source.
3. The optoelectronic module of claim 1 including a partially
reflective coating on a surface of the first transmissive region
facing away from the illumination source.
4. The optoelectronic module of claim 1 including a partially
reflective coating on each of opposite surfaces of the first
transmissive region.
5. The optoelectronic module of claim 1 including a reflective
coating on a surface of the light barrier facing the illumination
source.
6. The optoelectronic module of claim 1 wherein the optics member
includes a non-transmissive region separating the first and second
transmissive regions, the non-transmissive region having a
reflective coating on a surface facing the illumination source and
arranged such that some light from the illumination source is
reflected by the reflective coating toward the at least one
reference pixel.
7. An optoelectronic module comprising: an illumination source; a
sensor including spatially distributed detection pixels and at
least one reference pixel; an optics member disposed over the
illumination source and the sensor, the optics member having a
first transmissive region over the illumination source and a second
transmissive region over the detection pixels, wherein the first
transmissive region has a first coating on a first surface facing
the illumination source and a second coating on a second surface
facing away from the illumination source; a light barrier
separating an emission chamber of the module from a detection
chamber of the module, wherein the illumination source and the at
least one reference pixel are in the emission chamber, and wherein
the detection pixels are in the detection chamber; and wherein each
of the coatings is at least one of an optical filter coating, a
partially-reflective coating, an anti-reflective coating or a
non-transmissive coating.
8. The optoelectronic module of claim 7 wherein at least one the
first or second coating comprises black chrome.
9. The optoelectronic module of claim 7 including a respective
black chrome coating on each of opposite surfaces of the first
transmissive region.
10. The optoelectronic module of claim 7 wherein each of the one of
more surfaces of the first transmissive region has a black chrome
coating and an optical filter coating thereon.
11. The optoelectronic module of claim 7 further including a
passive optical element mounted on, or incorporated into, the first
transmissive window.
12. The optoelectronic module of claim 11 wherein the passive
optical element includes at least one of a reflective patch, a
diffractive optical element, or a refractive optical element.
Description
BACKGROUND
Some handheld computing devices such as smart phones can provide a
variety of different optical functions such as one-dimensional (1D)
or three-dimensional (3D) gesture detection, 3D imaging, proximity
detection, ambient light sensing, and/or front-facing
two-dimensional (2D) camera imaging.
TOF-based systems, for example, can provide depth and/or distance
information. In general, TOF systems are based on the
phase-measurement technique of emitted intensity-modulated light,
which is reflected by a scene. The reflected light is imaged onto a
sensor, and the photo-generated electrons are demodulated in the
sensor. Based on the phase information, the distance to a point in
the scene for each pixel is determined by processing circuitry
associated with the sensor.
Additionally, TOF-based systems can provide depth and/or distance
information via a pulse-measurement technique. The
pulse-measurement technique employs an emitter and sensor as above;
however, distance is determined by tallying the time for emitted
light to reflect back onto the sensor.
Integrating TOF sensors into devices such as smart phones, tablets
or other handheld devices, however, can be challenging for several
reasons. First, space in the host device typically is at premium.
Thus, there is a need to achieve accurate TOF sensors having a
relatively small height. Second, the size of the dies impacts
production costs. Accordingly, it is desirable to achieve TOF
sensors having a relatively small foot print.
While the foregoing issues also may be applicable to other types of
optical imaging or detection sensors, another potential problem is
more specific to TOF sensors. In particular, the distance
measurements obtained by the pixels should be robust against phase
delays caused, for example, by thermal drifting effects. To address
such concerns, in some TOF chips, a self-calibration of the TOF
distance measurement is achieved by providing reference pixels that
measure light from the illumination source. The use of such
reference pixels necessitates directing some of the light from the
illumination source to the reference pixels, which may need to be
separated optically from the active pixels used to measure the
distance to the scene.
TOF-based distance measurements via the pulsed-measurement
technique should be robust against thermal drifting effects. For
example, in some instances the precise time for commencement of the
initial emission of light from the emitter may be obscured by
thermal drifting effects.
SUMMARY
The present disclosure describes optical imaging and optical
detection modules that include sensors such as time-of-flight (TOF)
sensors.
Various implementations are described that, in some instances, can
help reduce the amount of optical cross-talk between the active
detection pixels and the reference pixels and/or can facilitate the
ability of the sensor to determine an accurate phase difference to
be used, for example, in distance calculations.
In one aspect, this disclosure describes an optoelectronic module
that includes an illumination source, a sensor including spatially
distributed detection pixels and at least one reference pixel, an
optics member disposed over the illumination source and the sensor,
and a light barrier separating an emission chamber of the module
from a detection chamber of the module. The optics member has a
first transmissive region over the illumination source and a second
transmissive region over the detection pixels. The illumination
source and the at least one reference pixel are in the emission
chamber, whereas the detection pixels are in the detection chamber.
Also, optoelectronic module includes at least one of: (i) a
partially reflective coating on a surface of the first transmissive
region over the illumination source or (ii) a reflective coating on
a surface of the emission chamber, wherein the coating is arranged
such that some light from the illumination source is reflected by
the coating toward the at least one reference pixel.
In another aspect, an optoelectronic module includes a coating on a
surface of the optic member's transmissive region over the
illumination source, wherein the coating is at least one of an
optical filter coating, a partially-reflective coating, an
anti-reflective coating or a non-transmissive coating.
In yet another aspect, an optoelectronic module includes one or
more micro lenses disposed over the detection pixels and/or the
reference pixel(s).
According to a further aspect, each of one or more detection and/or
reference pixels is at least partially surrounded laterally by a
shield of one or more layers that narrow an effective field of view
for the pixel.
In accordance with another aspect, an optoelectronic module
includes a printed circuit board, and an illumination source
mounted on or in the printed circuit board. The module further
includes spatially distributed detection pixels and at least one
reference pixel implemented in one or more semiconductor sensor
that are embedded within the printed circuit board.
A further aspect describes a method of determining a distance to an
object using a time-of-flight sensor that includes active
demodulation detection pixels and one or more reference pixels. The
method includes integrating the active demodulation detection
pixels during a first integration period and integrating the one or
more reference pixels during a second integration period different
from the first integration period. Signals are read out from the
active demodulation detection pixels during a first read-out period
after the first integration period, and signals are read out from
the one or more reference pixels during a second read-out period
after the second integration period.
As described in accordance with another aspect, an optoelectronic
module includes control logic configured to tune an integration
time of at the reference pixel(s).
Another aspect relates to a method of determining a distance to an
object using a time-of-flight sensor module that includes
demodulation detection pixels and one or more reference pixels. The
method includes measuring sensed values from a particular
demodulation detection pixel and from a particular reference pixel,
and determining a phase difference based, at least in part, on the
sensed values and based on stored sensitivity values, wherein the
sensitivity values are indicative of amounts of optical cross-talk
between the particular demodulation detection pixel and the
particular reference pixel. The module can include processing logic
to implement the method.
In yet another aspect, an optoelectronic module includes a
transmissive member disposed over the illumination source and the
sensor. A respective black chrome coating is on opposite surfaces
of the transmissive member, wherein each of the black chrome
coatings defines a transmissive window that allows light from the
illumination source to pass through to outside the module. Openings
are provided in a portion of the black chrome coating on a
sensor-side of the transmissive member in a vicinity of the at
least one reference pixel. In some cases, the presence of the black
chrome coating can enhance the amount of light reflected to the
reference pixels; providing part of the black chrome coating as a
pattern can be used to prevent an excessive amount of light from
being incident on the reference pixels.
Other aspects, features and advantages will be readily apparent
from the following detailed description, the accompanying drawings,
and the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates general operation of a TOF camera system.
FIG. 2 illustrates an example of an optoelectronic module according
to some implementations of the invention.
FIG. 3 illustrates another example of an optoelectronic module
according to some implementations of the invention.
FIG. 4 illustrates a further example of an optoelectronic module
according to some implementations of the invention.
FIGS. 5-7 illustrated additional examples of optoelectronic modules
according to some implementations of the invention.
FIGS. 8A-8D illustrate examples of integration timing diagrams.
FIG. 9 is a flow chart of a method for determining a phase
difference in some implementations of the invention.
FIG. 10 is a vector graph illustrating vectors to assist in
understanding the method of FIG. 9.
FIG. 11 illustrates another example of an optoelectronic module
according to some implementations of the invention.
DETAILED DESCRIPTION
As shown in FIG. 1, a TOF camera system 20 includes an illumination
source 22. Modulated emitted illumination light 24 from the source
22 is directed toward a scene 26 that includes one or more objects.
A fraction of the total optical power directed to the scene is
reflected back to the camera 20, through optics 28, and is detected
by a 3D imaging sensor 30. The sensor 30 includes a 2D pixel matrix
32 of demodulation pixels 34. Each pixel 34 is capable of
demodulating the impinging light signal 25 that is collected by the
optics 28 (e.g., a lens) and imaged onto the imaging sensor 30. An
electronics control unit 36 controls the timing of the illumination
module 22 and sensor 30 to enable its synchronous detection.
The demodulation values allow for each pixel 34 to compute the
time-of-flight, which, in turn, directly corresponds to the
distance information (R) of the corresponding point in the scene
26. The 2D gray scale image with the distance information can be
converted into a 3D image at the data output interface 38 that
includes an image processor and/or other control and processing
logic (e.g., microprocessor and/or other circuitry). The 3D image
can be displayed to a user, for example, on a display 40 or can be
used as machine vision input.
The time-of-flight (TOF) is obtained by demodulating the light
signals reflected from the scene 26 and that impinge on the active
pixels 34 of the sensor 30. Different modulation techniques are
known, for example pseudo-noise modulation, pulse modulation and
continuous modulation. The distance to the object for each pixel
then can be calculated based on the detected signals using known
techniques.
The sensor 30 can be implemented, for example as an integrated
semiconductor chip that also includes a region (e.g., a row) of
reference pixels 44. During operation, a fraction of the light from
the forward path of the illumination source 22 is fed back to one
or more reference pixels 44. The signals detected by the reference
pixels 44 can be used to re-calculate a zero-distance with every
frame, thereby facilitating self-calibration of the TOF distance
measurement. The sensor chip also can include, for example, control
logic, decoder logic and read-out logic.
FIG. 2 illustrates an example of an optoelectronic module 100 that
includes a light emission channel 102 and a light detection channel
104. A light emitter chip 106 and a TOF sensor chip 108 are mounted
on a first side of a printed circuit board (PCB) 110. The light
emitter 106 is an example of an illumination source. In some cases,
the light emitter 106 is operable to generate coherent,
directional, spectrally defined light emission. Examples of the
light emitter 106 are a laser diode or a vertical cavity surface
emitting laser (VCSEL).
An optics member 116 spans across the channels 102, 104 and
includes transmissive windows 122A, 122B that are substantially
transparent to a wavelength of light (e.g., infra-red radiation)
emitted by the emitter 106. In some instances, as shown in FIG. 2,
the emitter and detector windows 122A, 122B are separated from one
another by an opaque or substantially non-transmissive region 131
that forms part of the optics member 116. Light from the emitter
106 is directed out of the module through the emitter window 122A
and, if reflected by an object back toward the module's detection
channel 104, can be sensed by the TOF sensor 108.
The TOF sensor 108 can include an array of spatially distributed
light sensitive elements (e.g., active demodulation detection
pixels) 124 as well as one or more light sensitive reference pixels
128. Both the detection pixels 124 and the reference pixels 128 are
able to sense light at a wavelength emitted by the emitter 106. The
detection pixels 124 provide the primary signals for determining
the distance to an object outside the module. Signals from the
reference pixels 128 can be used to compensate for drift and/or to
provide a zero distance measurement. The sensor 108 can be
implemented, for example, using charge-coupled device (CCD) or
complementary metal oxide semiconductor (CMOS) technologies. In
some cases, the reference pixels 128 are located on the same sensor
chip as the detection pixels 124, although in other cases, as
discussed below, they may be located on different chips. In some
instances, there may be an array of reference pixels (e.g., a
single line of pixels or multiple lines of pixels). Typically,
there are many fewer reference pixels 128 than detection pixels
124.
The emitter 106 and the TOF sensor 108 can be connected
electrically to the PCB 110, for example, by conductive pads or
wire bonds. The PCB 110, in turn, can be connected electrically to
other components within a host device (e.g., a smart phone or
tablet).
In the example of FIG. 2, a vertical shield (i.e., light barrier)
130 extends between the optics member 116 and the surface of the
TOF sensor 108. The shield 130, which substantially attenuates the
light or is non-transparent (i.e., opaque) to the light emitted by
the emitter 106, is disposed such that detection pixels 124 are
located to one side of the shield and the reference pixels are
located to the other side of the shield. The reference pixels 128
are thus disposed in the emission chamber 102 on the same side of
the shield 130 as the emitter 106. The detection pixels 124,
however, are disposed on the other side of the shield 130 in the
detection chamber 104. This arrangement allows a small amount of
light from the emitter 106 to be reflected by the transmissive
window 122A for sensing by the reference pixels 128 without
introducing optical cross-talk from the emission chamber 102 to the
detection pixels 124.
In the illustrated example of FIG. 2, the non-transmissive section
131 of the optics member 116 between the transmissive windows 122A,
122B can be composed of the same material as the light barrier
130.
In some implementations, one or more surfaces of the emission
chamber 102 are coated with an optical filter, a
partially-reflective coating, an anti-reflective coating and/or an
anti-scratch coating. For example, the emitter window 122A can
include a coating 132, such as an optical filter coating, an
anti-reflective coating and/or a non-transparent coating (e.g.,
black chrome), disposed on its top or bottom side (or on both
sides). In some situations, both sides of the emitter window 122A
have the same coating provided thereon. In other cases, the top and
bottom sides of the emitter window 122A have different coatings.
Further, in some instances, one or both sides may have two (or
more) different coatings. The coating(s) may be partially
reflective to some wavelengths of light (i.e., wavelength(s) that
can be detected by the reference pixels). Thus, for example, some
of the light reflected by the emitter window 122A can be incident
on the reference pixels 128. In some implementations, a passive
optical element is mounted on, or incorporated into, the emitter
window 122A. Examples of such a passive optical element include a
reflective patch, a diffractive optical element, and/or a
refractive optical element such as a prism.
Instead of, or in addition to, providing a partially reflective
coating on a surface of the emitter window 122A, a reflective
coating 133 can be provided on the surface of the light barrier 130
or the non-transmissive region 131 of the optics member 116. Such a
reflective coating can help direct some of the emitter light toward
the reference pixels 128.
When light from the emitter 106 is reflected by the emitter window
122A or other surface of the emission chamber 102 toward the
reference pixels 128, such light preferably is not incident on the
detection pixels 124. In some cases, such as the implementation of
FIG. 2, the light barrier 130 helps prevent light reflected by the
emitter window 122A from being incident on the detection pixels
124.
Although the light barrier 130 can help reduce optical cross-talk
between the detection pixels 124 and the reference pixels 128,
incorporating the light barrier into the module 100 may increase
the overall footprint and/or height of the module. Thus, in some
instances, it may be desirable to provide the advantages of using
reference pixels 128 without the need for the light barrier 130. In
such cases, other techniques can be used to address the issue of
optical cross-talk. Examples of these other techniques are
described below and can be used together with, or instead of, the
light barrier 130.
In the implementation of FIG. 2, the detection pixels 124 may have
a relatively broad field of view (FOV) such that they sense
incoming light from a broad angle. In some instances (e.g., in a
module without the light barrier 130), it can be advantageous to
narrow the FOV of the detection pixels 124 to reduce the amount of
optical cross-talk sensed by the pixels 124. This can be achieved,
for example, by providing one or more micro lenses 140 over the
detection pixels 124 (sec FIG. 3).
In some instances, a micro lens 140A also can be placed over the
reference pixels 128. By displacing the micro lens 140A slightly in
the direction of the emitter 106, the reference pixels 128 can
collect more light from the emitter. Such an arrangement also can
help reduce the amount of optical cross-talk sensed by the
reference pixels 128. In some implementations, the micro lens over
the reference pixels is omitted.
In some cases, providing micro lenses 140 to narrow the FOV of the
detection pixels 124 can obviate the need for a light barrier 130
(see FIG. 2) to prevent light reflected by the emitter window 122A
from being incident on the detection pixels 124. In implementations
that do not include the light barrier 130, the section 131 of the
optics member 116 that substantially attenuates or is
non-transparent to light emitted by the emitter 106 also can be
omitted such that the transmissive widows 122A, 122B are not
separated from one another by an opaque or non-transparent section
131. Eliminating the need for the light barrier 130 can help reduce
the overall size of the module, which can be advantageous for
applications in which the module is to be integrated into a
handheld device such as a smart phone or tablet in which space is
at a premium.
In some implementations, stacks 144 can be provided as shields
around one or more of the pixels 124, 128 (see FIG. 4). The stacks
144, which can be composed, for example, of metal or other layers,
can help define the FOV for the detection pixels 124 and can help
reduce optical cross-talk caused by emitter light reflected toward
the detection pixels. Likewise, the stack 144 around the reference
pixels 128 can help ensure that light reflected by the emitter
window 122A is incident on the reference pixels, but that light
reflected by an object outside the module is not incident on the
reference pixels. A respective stack 144 can partially, or
completely, surround each individual pixel 124, 128 laterally.
Further, the stacks 144 can be provided instead of, or in addition
to, the micro lenses 140, 142 of FIG. 3.
In some instances, as illustrated in FIG. 5, the sensor chip 108
can be embedded within layers of the PCB 110. Such an arrangement
can facilitate optical separation of the reference pixels 128 from
the active detection pixels 124, thereby reducing optical
cross-talk. Further, one or more layers 110A of the PCB stack 110
itself can be used to provide optical separation between the
reference and detection pixels. By embedding the sensor chip 108
within the PCB 110, design of the light barrier can be made easier
because considerations related to material and mechanical stress
tend to be less important in view of the inherent protection of the
sensor 108 by the PCB 110. Further, by using layers 110A of the PCB
110 to provide the optical separation, the overall height of the
module can be kept relatively small.
In the foregoing examples (including the example of FIG. 5), a
single sensor chip 108 includes both the active detection pixels
124 and the reference pixels 128 (as well as the control logic,
decoder logic and read-out logic). In other implementations, the
reference pixels 128 are integrated into a chip 108A separate from
the chip 108B containing the active detection pixels 124 (see FIG.
6). Each of the chips 108A, 108B, which can be embedded within the
PCB 110, also can include appropriate control logic, decoder logic
and/or read-out logic. Embedding the sensor chip(s) within the PCB
layers can be combined, for example, with other techniques
described here (e.g., a partially reflective or other coating on a
surface of the emission chamber; the addition of micro lenses 140,
142 over the pixels; the addition of reflective layers 144 around
the pixels).
In some instances, in addition to embedding the sensor chip(s)
108A, 108B in the PCB 110, the emitter chip 106 also can be
embedded with the PCB layers (see FIG. 7).
Embedding the sensor and/or emitter chips 108, 106 within the PCB
110 can achieve other advantages in some instances. For example,
the need for bonding wires can be obviated. Eliminating the need
for bonding wires, which tend to be vulnerable to mechanical
vibrations, can be useful. Further, bonding wires introduce
parasitic capacitances and inductances, which make high frequency
applications more challenging. Thus, eliminating the need for
bonding wires can facilitate high frequency applications.
Embedding the sensor and/or emitter chips 108, 106 within the PCB
110 also can help protect the chips better in some implementations
because only the passivated chip surfaces of the chips are
exposed.
In some implementations, the active detection pixels 124 and the
reference pixels 128 may have integration times (i.e., exposure
times) that occur simultaneously. However, in other cases, the
module can use multiple non-overlapping integration times (e.g.,
one for the active detection pixels 124 and another for the
reference pixels 128). An example of the timing for such an
implementation is illustrated in FIG. 8A. In some cases, a variable
integration period 152 can be used for the active detection pixels
124, whereas a fixed integration period 154 can be used for the
reference pixels 128. The exposure time for the detection pixels
124 can be adjusted, for example, to reduce the signal-to-noise
(S/N) ratio based on the level of signals reflected by objects in
the scene 26. The active pixels 124 can be read out, for example,
during a first period 156, and the reference pixels 128 can be read
out during a second period 158. The duration of the read out time
may be a function, for example, of the pixel(s) size.
In some implementations, the sensor's control circuitry is
configured to tune the integration times of the reference pixels so
as achieve an affective sensitivity for the pixels. Varying the
integration times for the reference pixels can provide an
alternative to varying the aperture size of the pixels. For
example, a longer integration period may correspond to pixel having
a relatively large aperture, whereas a smaller integration period
may correspond to a pixel having a relatively small aperture. In
some cases, tunable integration times can be used to initiate (or
end) the reference pixel integration period at a specified time
relative to the integration period of the active detection pixels.
FIGS. 8B-8C illustrates examples that can be achieved using tunable
integration times for the reference pixels. As illustrated in the
example of FIG. 8B, the reference pixel integration 162 occurs
during the middle of the active pixel integration 164. In contrast,
as shown in the example of FIG. 8C, the reference pixel integration
occurs for short periods 166, 168 at the beginning and at the end
of the active pixel integration period 164, which can result in
averaging of the thermal phase shift of the emitter 106 that occurs
over time. In some instances, a particular reference pixel is
integrated during both integration periods 166, 168. In other
cases, a first reference pixel may be integrated during the first
integration period 166, and a different second pixel may be
integrated during the second integration period 168.
In some cases, such as where the sensor 108 has multiple reference
pixels 128, the sensor's control circuitry can control the
reference pixels such that different pixels have integration
periods of different duration. FIG. 8D illustrates an example, in
which a first reference pixel (or subset of reference pixels)
integrates during a first integration period 172 having a first
duration, a second reference pixel (or subset of reference pixels)
integrates during a second integration period 174 having a second
duration longer than the first integration period, and a third
reference pixel (or subset of reference pixels) integrates during a
third integration period 176 having a third duration longer than
the second integration period. In the illustrated example, each of
the pixels is integrated at a time near the middle of the
integration period for the active pixels, although this need not be
the case for all implementations. Further, each of the integration
periods 172, 174, 176 is shorter than the integration period 164
for the active pixels.
The dynamic range of the sensor depends on the maximum amount of
charge that each pixel can accumulate. Thus, for some
implementations, the dynamic range of the sensor can be increased
by increasing the maximum charge capability of the reference pixels
128.
In the foregoing examples, various techniques are described to help
isolate the detection pixels 124 and reference pixels 128 optically
from one another so as to reduce optical cross-talk (i.e., to
reduce the amount of light reflected, for example, by the emission
window 122A that is sensed by the detection pixels 124, and to
reduce the amount of light reflected by an object in the scene 26
that is sensed by the reference pixels 128). Nevertheless, as
described below, in some implementations, even when such optical
cross-talk is present, it is possible to determine the phase
difference, and thus the distance to an object in the scene.
For example, based on prior calibrations of the imaging system, it
can be determined that a particular detection pixel 124 has a first
sensitivity a defined as the ratio of two sensed signals
(Aref/Bref) each of which results from light reflected by the
emission window 122A (or other surface of the emission chamber)
(FIG. 9, block 200). In this case, Aref represents the component of
light sensed by the detection pixel 124 resulting from light
reflected by the emission window 122A (or other surface of the
emission channel), and Bref represents the component of light
sensed by a particular reference pixel 128 resulting from the light
reflected by the emission window 122A (or other surface of the
emission channel). Likewise, based on prior calibrations of the
imaging system, it can be determined that the reference pixel 128
has a second sensitivity 13 defined as the ratio of two sensed
signals (Aobj/Bobj) each of which results from light reflected by
an object in the scene 26. In this case, Aobj represents the
component of light sensed by the reference pixel 128 resulting from
light reflected by the object in the scene 26, and Bobj represents
the component of light sensed by the detection pixel 124 resulting
from light reflected by the object in the scene. In general, each
of .alpha. and .beta. will have respective values between 0 and 1,
and typically should have values closer to 0. Thus, the
sensitivities .alpha. and .beta. represent indications of the
optical cross-talk that occurs between the reference and active
detection pixels. The values for .alpha. and .beta. can be stored
by logic or memory in the imaging system (FIG. 9, block 202).
In the following discussion, it is assumed that the two pixels
(i.e., the detection pixel and the reference pixel) have different
sensitivities from one another (i.e., that a and (are different).
Signals sensed by each of the two pixels are measured and read out
to obtain a reference vector {right arrow over (R.sub.ref)} and an
object vector {right arrow over (R.sub.obj)}, respectively (see
FIG. 9, block 204; FIG. 10). Each of these vectors represents the
total amount of light detected, respectively, by the reference
pixel 128 or the detection pixel 124, and thus each vector
represents the sum of the two signal components sensed by the
particular pixel (i.e., a first component of light sensed by the
pixel resulting from the light reflected by the emission window
122A (or other surface of the emission chamber) and a second
component of light sensed by the same pixel resulting from light
reflected by an object in the scene 26). Although the two signal
components are superposed on one another, the phase .phi., and thus
the distance to the actual object in the scene, can be calculated
by the sensor's processing logic as follows: .phi.=phase({right
arrow over (obj)}/{right arrow over (ref)}), where: {right arrow
over (obj)}=({right arrow over (R.sub.obj)}-.alpha..times.{right
arrow over (R.sub.ref)})/(1-.alpha..times..beta.) {right arrow over
(ref)}=({right arrow over (R.sub.ref)}-.beta..times.{right arrow
over (R.sub.obj)})/(1-.alpha..times..beta.) (See FIG. 9, block 206)
To obtain advantageous use of the foregoing technique for
determining the phase difference, the sensitivities .alpha. and
.beta. for the various pixels should be substantially independent
of the environment in which the sensor module is located.
FIG. 11 illustrates a portion of an optoelectronic module that has
a sensor including reference pixels 128. In this example, the
optics member 116 includes a transmissive cover (e.g., a cover
glass) 122 above the PCB substrate 110. Both sides of the cover
glass 122 are coated, for example, with optical filters 121A and
121B, respectively. The optical filters 121A and 121B can filter a
particular wavelength or range of wavelengths of light emitted by
the emitter 106. Further the optical filters 121A, 121B are coated,
for example, with black chrome 184A, 184B to prevent cross-talk via
the cover glass 122. Respective parts of the filters 121A, 121B are
not covered with the black chrome so as to define a transmissive
window 122C that allows light from the emitter 106 to pass out of
the module. The presence of the black chrome coating 184B on the
sensor-side of the optics member 116 also can help enhance the
amount of light that reflects from the optical filter 121B toward
the reference pixels 128. In some cases, to reduce the likelihood
that too much emitter light is reflected by the black chrome layer
184B onto the reference pixels 128, the black chrome layer 184B can
be provided as a pattern 185B with openings (e.g., dots, lines,
concentric circles) so as to reduce the amount of light incident on
the reference pixels 128. Further, the black chrome layer 184A can
be provided as a pattern 185A with openings (e.g. dots, lines,
concentric circles) so as to reduce the amount of light incident on
the reference pixels 128. As illustrated in the example of FIG. 11,
the patterns 185A, 185B include openings 186A, 186B where there is
no black chrome. Thus, while the presence of the black chrome
coating 184A, 184B can enhance the amount of light reflected to the
reference pixels 128, providing part of the black chrome coating as
a pattern 185A, 185B can be used to prevent too much light from
being incident on the reference pixels 128. In some
implementations, the black chrome layers 184A, 184B need not be
provided as patterns 185A, 185B with openings. For example, the
chrome layers 184A, 1854 may be provided as a single opening such
as a circle, square or other geometric shape.
Use of the features and techniques in the foregoing implementations
can result, in some instances, in small sensor modules (i.e.,
having a small height and/or a small footprint). Further, the
foregoing implementations can help reduce or eliminate optical
cross-talk. Such small modules can be integrated advantageously
into devices such as smart phones, tablets, and other host devices
in which space is at a premium.
Various modifications can be made to the foregoing examples.
Further, features from the different examples can, in some
instances, be integrated in the same module. Other implementations
are within the scope of the claims.
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